This project is intended to improve our understanding of the mechanism by which calcium is transported through the phospholipid bilayer of the sarcoplasmic reticulum. Chemical crosslinking and freeze-fracture electron microscopy will be used to look for changes in oligomeric state of the sarcoplasmic reticulum membrane proteins (in particular the 100,000 dalton Ca2 ion-activated ATPase protein) that accompany calcium accumulation. In cardiac sarcoplasmic reticulum, an additional control of calcium transport is provided by protein kinase mediated phosphorylation of the 22,000 dalton protein, phospholamban. Both cAMP-dependent protein kinase and an endogenous calmodulin-activated protein kinase, phosphorylate phospholamban and activate calcium uptake. The associations between these kinases, kinase substrate (phospholamban) and the ATPase will be determined. The goal of this project is to show whether ionic channels in membranes can be regulated by changes in monomer-oligomer equilibria of membrane proteins.